Method and device for transmitting event information in V2X communication

ABSTRACT

Provided are a method by which a device performs V2X communication in a wireless communication system, and a device for supporting the same. The device receives event termination information from a terminal and can transmit the event termination information to a neighboring device. The terminal is provided in a vehicle for V2X communication, and the event termination information can be information indicating that an event occurring in the terminal has been terminated.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage filing under 35 U.S.C. 371 of International Application No. PCT/KR2016/003098, filed on Mar. 28, 2016, which claims the benefit of U.S. Provisional Application No. 62/138,400, filed on Mar. 26, 2015, the contents of which are all hereby incorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a wireless communication system, and more particularly, to a method by which a base station or a road side unit (RSU) transmits event information in vehicle-to-infra/vehicle/nomadic (V2X) communication in the wireless communication system, and a device supporting the method.

Related Art

3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) that is an advancement of UMTS (Universal Mobile Telecommunication System) is being introduced with 3GPP release 8. In 3GPP LTE, OFDMA (orthogonal frequency division multiple access) is used for downlink, and SC-FDMA (single carrier-frequency division multiple access) is used for uplink. The 3GPP LTE adopts MIMO (multiple input multiple output) having maximum four antennas. Recently, a discussion of 3GPP LTE-A (LTE-Advanced) which is the evolution of the 3GPP LTE is in progress.

In recent years, there is growing interest in a Device-to-Device (D2D) technology performing direct communication between devices. In particular, the D2D is attracting attention as a communication technology for a public safety network. A commercial communication network has been rapidly changed to the LTE but a current public safety network is based on a 2G technology in a collision problem and a cost side with an existing communication standard. Request for the technology clearance and an improved service induces an effort to improve the public safety network.

The public safety network has high service requirements (reliability and security) as compared with a commercial communication network. In particular, when coverage of cellular communication is insufficient or is not used, there is a need for direct signal transmission/reception between devices, that is, an D2D operation.

The D2D operation may be signal transmission/reception between adjacent devices to have various advantages. For example, a D2D terminal may perform data communication with a high transmission rate and low delay. Further, the D2D operation may distribute traffic converged in a base station. If the D2D terminal serves as a relay, the D2D terminal may serve to extend coverage of a base station.

Vehicle-to-infra/vehicle/nomadic (V2X) is a technique which adds mobility to a D2D technique to persistently communicate with a road infrastructure or other vehicles while driving a vehicle, thereby exchanging and sharing useful information such as a traffic condition or the like. V2X networking is roughly divided into three categories, that is, vehicle-to-infrastructure (hereinafter, V2I), vehicle-to-vehicle (hereinafter, V2V), and vehicle-to-nomadic devices (hereinafter, V2N) communication. It is expected that vehicle-to-grid (V2G) is added thereto in a near future as another type of communication classification with regard to charging of electric vehicles which are recently drawing attention.

SUMMARY OF THE INVENTION

When an event such as a vehicle collision occurs, a base station or road side unit (RSU) in which the event has occurred may periodically broadcast information related to the event to a terminal in coverage so that the event is indicated rapidly to an adjacent region. However, since the base station or the RSU cannot know an event termination time if the event is terminated, it may be problematic for the base station or the RSU to continuously broadcast the event-related information after the event is terminated. Further, the base station or the RSU may need to propagate an event occurring according to a range of the event-related information to a wide region. Therefore, the present invention proposes a method by which the base station or the RSU provides information regarding an event termination to a neighboring base station or a neighboring RSU, and a device supporting the method. In addition, the present invention proposes a method by which the base station or the RSU provides event-related information to a neighboring base station or a neighboring RSU to extend a range of providing information, and a device supporting the method.

According to an embodiment, there is provided a method by which a device performs vehicle-to-infra/vehicle/nomadic (V2X) communication in a wireless communication system. The method may include: receiving event termination information from a terminal; and transmitting the event termination information to a neighboring device. The terminal may be a terminal installed in a vehicle for V2X communication. The event termination information may be information indicating that an event occurring in the terminal has been terminated.

The device may be any one of a base station and an RSU.

The event termination information may be transmitted by being comprised in at least any one of an event termination indication message, an existing message, a new IE included in a new message, or a new IE comprised in the existing message.

The event termination information may be transmitted by being included in at least any one of a deallocate TMGI request message, a modify MBMS bearer request message, a deactivate MBMS bearer request message, an MBMS session update request message, an MBMS session stop request message, and a new message.

The method may further include: receiving event occurrence information from the terminal; and transmitting the event occurrence information to the neighboring device. The event occurrence information may be information indicating that an event occurs in the terminal.

The method may further include, if the device which has received the event termination information has the event occurrence information, stopping transmission of the event occurrence information to the neighboring device.

The method may further include: generating a hop level; and transmitting the hop level to the neighboring device. The hop level may indicate the number of devices via which the event termination information passes.

According to another embodiment, there is provided a method by which a first device performs V2X communication in a wireless communication system. The method may include: receiving event occurrence type information and a hop level from a second device; modifying the received hop level; comparing the modified hop level with a predefined value; if the modified hop level is equal to the predefined value, broadcasting the event occurrence type information to a terminal in coverage of the first device; and if the modified hop level is different from the predefined value, transmitting the event occurrence type information and the modified hope level to a third device. The hop level may indicate the number of devices via which the event occurrence type information passes. The terminal may be a terminal installed in a vehicle for V2X communication. The second device and the third device may be connected to the first device through X2.

The modifying of the hop level may be decreasing of the hop level by 1. The predefined value may be 0.

The event occurrence type information may be information regarding a range in which the event occurrence information is propagated.

The event occurrence type information may be information regarding a range in which the event termination information is propagated.

The first device, the second device, and the third device may be any one of a base station and an RSU.

The event occurrence type information and the hop level may be transmitted by being included in at least any one of an event indication message, a deallocate TMGI request message, a modify MBMS bearer request message, a deactivate MBMS bearer request message, an MBMS session update request message, an MBMS session stop request message, and a new message.

According to another embodiment, a device for performing V2X communication in a wireless communication system may include: a memory; a transceiver; and a processor operatively coupled to the memory and the transceiver. The processor may be configured for: controlling the transceiver to receive event termination information from a terminal; and controlling the transceiver to transmit the event termination information to a neighboring device. The terminal may be a terminal installed in a vehicle for V2X communication. The event termination information may be information indicating that an event occurring in the terminal has been terminated.

The device may be any one of a base station and an RSU.

Event occurrence information can be prevented from being unnecessarily transmitted to a neighboring base station or a neighboring RSU.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows LTE system architecture.

FIG. 2 shows a control plane of a radio interface protocol of an LTE system.

FIG. 3 shows a user plane of a radio interface protocol of an LTE system.

FIG. 4 shows a procedure in which UE that is initially powered on experiences a cell selection process, registers it with a network, and then performs cell reselection if necessary.

FIG. 5 shows an RRC connection establishment procedure.

FIG. 6 shows an RRC connection reconfiguration procedure.

FIG. 7 shows an RRC connection re-establishment procedure.

FIG. 8 shows a reference structure for a ProSe.

FIG. 9 shows arrangement examples of terminals performing ProSe direct communication and cell coverage.

FIG. 10 shows a user plane protocol stack for the ProSe direct communication.

FIG. 11 shows a PC 5 interface for D2D discovery.

FIG. 12 shows an embodiment of a ProSe direct discovery procedure.

FIG. 13 shows another embodiment of a ProSe direct discovery procedure.

FIG. 14 shows a problem which may occur in the conventional V2X communication.

FIG. 15 shows a method by which a base station or an RSU indicates an event termination according to an embodiment of the present invention.

FIG. 16 shows a method by which a base station or an RSU indicates an event type and a hop level according to an embodiment of the present invention.

FIG. 17 shows a path of transmitting a message between a base station or an RSU and a neighboring base station or a neighboring RSU according to an embodiment of the present invention.

FIG. 18 is a block diagram of a method by which a device performs V2X communication according to an embodiment of the present invention.

FIG. 19 is a block diagram of a method by which a device performs V2X communication according to an embodiment of the present invention.

FIG. 20 is a block diagram illustrating a wireless communication system according to the embodiment of the present invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The technology described below can be used in various wireless communication systems such as code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), etc. The CDMA can be implemented with a radio technology such as universal terrestrial radio access (UTRA) or CDMA-2000. The TDMA can be implemented with a radio technology such as global system for mobile communications (GSM)/general packet ratio service (GPRS)/enhanced data rate for GSM evolution (EDGE). The OFDMA can be implemented with a radio technology such as institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, evolved UTRA (E-UTRA), etc. IEEE 802.16m is evolved from IEEE 802.16e, and provides backward compatibility with a system based on the IEEE 802.16e. The UTRA is a part of a universal mobile telecommunication system (UMTS). 3rd generation partnership project (3GPP) long term evolution (LTE) is a part of an evolved UMTS (E-UMTS) using the E-UTRA. The 3GPP LTE uses the OFDMA in a downlink and uses the SC-FDMA in an uplink. LTE-advanced (LTE-A) is an evolution of the LTE.

For clarity, the following description will focus on LTE-A. However, technical features of the present invention are not limited thereto.

FIG. 1 shows LTE system architecture. The communication network is widely deployed to provide a variety of communication services such as voice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, the LTE system architecture includes one or more user equipment (UE; 10), an evolved-UMTS terrestrial radio access network (E-UTRAN) and an evolved packet core (EPC). The UE 10 refers to a communication equipment carried by a user. The UE 10 may be fixed or mobile, and may be referred to as another terminology, such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a wireless device, etc.

The E-UTRAN includes one or more evolved node-B (eNB) 20, and a plurality of UEs may be located in one cell. The eNB 20 provides an end point of a control plane and a user plane to the UE 10. The eNB 20 is generally a fixed station that communicates with the UE 10 and may be referred to as another terminology, such as a base station (BS), a base transceiver system (BTS), an access point, etc. One eNB 20 may be deployed per cell. There are one or more cells within the coverage of the eNB 20. A single cell is configured to have one of bandwidths selected from 1.25, 2.5, 5, 10, and 20 MHz, etc., and provides downlink or uplink transmission services to several UEs. In this case, different cells can be configured to provide different bandwidths.

Hereinafter, a downlink (DL) denotes communication from the eNB 20 to the UE 10, and an uplink (UL) denotes communication from the UE 10 to the eNB 20. In the DL, a transmitter may be a part of the eNB 20, and a receiver may be a part of the UE 10. In the UL, the transmitter may be a part of the UE 10, and the receiver may be a part of the eNB 20.

The EPC includes a mobility management entity (MME) which is in charge of control plane functions, and a system architecture evolution (SAE) gateway (S-GW) which is in charge of user plane functions. The MME/S-GW 30 may be positioned at the end of the network and connected to an external network. The MME has UE access information or UE capability information, and such information may be primarily used in UE mobility management. The S-GW is a gateway of which an endpoint is an E-UTRAN. The MME/S-GW 30 provides an end point of a session and mobility management function for the UE 10. The EPC may further include a packet data network (PDN) gateway (PDN-GW). The PDN-GW is a gateway of which an endpoint is a PDN.

The MME provides various functions including non-access stratum (NAS) signaling to eNBs 20, NAS signaling security, access stratum (AS) security control, Inter core network (CN) node signaling for mobility between 3GPP access networks, idle mode UE reachability (including control and execution of paging retransmission), tracking area list management (for UE in idle and active mode), P-GW and S-GW selection, MME selection for handovers with MME change, serving GPRS support node (SGSN) selection for handovers to 2G or 3G 3GPP access networks, roaming, authentication, bearer management functions including dedicated bearer establishment, support for public warning system (PWS) (which includes earthquake and tsunami warning system (ETWS) and commercial mobile alert system (CMAS)) message transmission. The S-GW host provides assorted functions including per-user based packet filtering (by e.g., deep packet inspection), lawful interception, UE Internet protocol (IP) address allocation, transport level packet marking in the DL, UL and DL service level charging, gating and rate enforcement, DL rate enforcement based on APN-AMBR. For clarity MME/S-GW 30 will be referred to herein simply as a “gateway,” but it is understood that this entity includes both the MME and S-GW.

Interfaces for transmitting user traffic or control traffic may be used. The UE 10 and the eNB 20 are connected by means of a Uu interface. The eNBs 20 are interconnected by means of an X2 interface. Neighboring eNBs may have a meshed network structure that has the X2 interface. The eNBs 20 are connected to the EPC by means of an S1 interface. The eNBs 20 are connected to the MME by means of an S1-MME interface, and are connected to the S-GW by means of S1-U interface. The S1 interface supports a many-to-many relation between the eNB 20 and the MME/S-GW.

The eNB 20 may perform functions of selection for gateway 30, routing toward the gateway 30 during a radio resource control (RRC) activation, scheduling and transmitting of paging messages, scheduling and transmitting of broadcast channel (BCH) information, dynamic allocation of resources to the UEs 10 in both UL and DL, configuration and provisioning of eNB measurements, radio bearer control, radio admission control (RAC), and connection mobility control in LTE ACTIVE state. In the EPC, and as noted above, gateway 30 may perform functions of paging origination, LTE IDLE state management, ciphering of the user plane, SAE bearer control, and ciphering and integrity protection of NAS signaling.

FIG. 2 shows a control plane of a radio interface protocol of an LTE system. FIG. 3 shows a user plane of a radio interface protocol of an LTE system.

Layers of a radio interface protocol between the UE and the E-UTRAN may be classified into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lower three layers of the open system interconnection (OSI) model that is well-known in the communication system. The radio interface protocol between the UE and the E-UTRAN may be horizontally divided into a physical layer, a data link layer, and a network layer, and may be vertically divided into a control plane (C-plane) which is a protocol stack for control signal transmission and a user plane (U-plane) which is a protocol stack for data information transmission. The layers of the radio interface protocol exist in pairs at the UE and the E-UTRAN, and are in charge of data transmission of the Uu interface.

A physical (PHY) layer belongs to the L1. The PHY layer provides a higher layer with an information transfer service through a physical channel. The PHY layer is connected to a medium access control (MAC) layer, which is a higher layer of the PHY layer, through a transport channel. A physical channel is mapped to the transport channel. Data is transferred between the MAC layer and the PHY layer through the transport channel. Between different PHY layers, i.e., a PHY layer of a transmitter and a PHY layer of a receiver, data is transferred through the physical channel using radio resources. The physical channel is modulated using an orthogonal frequency division multiplexing (OFDM) scheme, and utilizes time and frequency as a radio resource.

The PHY layer uses several physical control channels. A physical downlink control channel (PDCCH) reports to a UE about resource allocation of a paging channel (PCH) and a downlink shared channel (DL-SCH), and hybrid automatic repeat request (HARQ) information related to the DL-SCH. The PDCCH may carry a UL grant for reporting to the UE about resource allocation of UL transmission. A physical control format indicator channel (PCFICH) reports the number of OFDM symbols used for PDCCHs to the UE, and is transmitted in every subframe. A physical hybrid ARQ indicator channel (PHICH) carries an HARQ acknowledgement (ACK)/non-acknowledgement (NACK) signal in response to UL transmission. A physical uplink control channel (PUCCH) carries UL control information such as HARQ ACK/NACK for DL transmission, scheduling request, and CQI. A physical uplink shared channel (PUSCH) carries a UL-uplink shared channel (SCH).

A physical channel consists of a plurality of subframes in time domain and a plurality of subcarriers in frequency domain. One subframe consists of a plurality of symbols in the time domain. One subframe consists of a plurality of resource blocks (RBs). One RB consists of a plurality of symbols and a plurality of subcarriers. In addition, each subframe may use specific subcarriers of specific symbols of a corresponding subframe for a PDCCH. For example, a first symbol of the subframe may be used for the PDCCH. The PDCCH carries dynamic allocated resources, such as a physical resource block (PRB) and modulation and coding scheme (MCS). A transmission time interval (TTI) which is a unit time for data transmission may be equal to a length of one subframe. The length of one subframe may be 1 ms.

The transport channel is classified into a common transport channel and a dedicated transport channel according to whether the channel is shared or not. A DL transport channel for transmitting data from the network to the UE includes a broadcast channel (BCH) for transmitting system information, a paging channel (PCH) for transmitting a paging message, a DL-SCH for transmitting user traffic or control signals, etc. The DL-SCH supports HARQ, dynamic link adaptation by varying the modulation, coding and transmit power, and both dynamic and semi-static resource allocation. The DL-SCH also may enable broadcast in the entire cell and the use of beamforming. The system information carries one or more system information blocks. All system information blocks may be transmitted with the same periodicity. Traffic or control signals of a multimedia broadcast/multicast service (MBMS) may be transmitted through the DL-SCH or a multicast channel (MCH).

A UL transport channel for transmitting data from the UE to the network includes a random access channel (RACH) for transmitting an initial control message, a UL-SCH for transmitting user traffic or control signals, etc. The UL-SCH supports HARQ and dynamic link adaptation by varying the transmit power and potentially modulation and coding. The UL-SCH also may enable the use of beamforming. The RACH is normally used for initial access to a cell.

A MAC layer belongs to the L2. The MAC layer provides services to a radio link control (RLC) layer, which is a higher layer of the MAC layer, via a logical channel. The MAC layer provides a function of mapping multiple logical channels to multiple transport channels. The MAC layer also provides a function of logical channel multiplexing by mapping multiple logical channels to a single transport channel. A MAC sublayer provides data transfer services on logical channels.

The logical channels are classified into control channels for transferring control plane information and traffic channels for transferring user plane information, according to a type of transmitted information. That is, a set of logical channel types is defined for different data transfer services offered by the MAC layer. The logical channels are located above the transport channel, and are mapped to the transport channels.

The control channels are used for transfer of control plane information only. The control channels provided by the MAC layer include a broadcast control channel (BCCH), a paging control channel (PCCH), a common control channel (CCCH), a multicast control channel (MCCH) and a dedicated control channel (DCCH). The BCCH is a downlink channel for broadcasting system control information. The PCCH is a downlink channel that transfers paging information and is used when the network does not know the location cell of a UE. The CCCH is used by UEs having no RRC connection with the network. The MCCH is a point-to-multipoint downlink channel used for transmitting MBMS control information from the network to a UE. The DCCH is a point-to-point bi-directional channel used by UEs having an RRC connection that transmits dedicated control information between a UE and the network.

Traffic channels are used for the transfer of user plane information only. The traffic channels provided by the MAC layer include a dedicated traffic channel (DTCH) and a multicast traffic channel (MTCH). The DTCH is a point-to-point channel, dedicated to one UE for the transfer of user information and can exist in both uplink and downlink. The MTCH is a point-to-multipoint downlink channel for transmitting traffic data from the network to the UE.

Uplink connections between logical channels and transport channels include the DCCH that can be mapped to the UL-SCH, the DTCH that can be mapped to the UL-SCH and the CCCH that can be mapped to the UL-SCH. Downlink connections between logical channels and transport channels include the BCCH that can be mapped to the BCH or DL-SCH, the PCCH that can be mapped to the PCH, the DCCH that can be mapped to the DL-SCH, and the DTCH that can be mapped to the DL-SCH, the MCCH that can be mapped to the MCH, and the MTCH that can be mapped to the MCH.

An RLC layer belongs to the L2. The RLC layer provides a function of adjusting a size of data, so as to be suitable for a lower layer to transmit the data, by concatenating and segmenting the data received from an upper layer in a radio section. In addition, to ensure a variety of quality of service (QoS) required by a radio bearer (RB), the RLC layer provides three operation modes, i.e., a transparent mode (TM), an unacknowledged mode (UM), and an acknowledged mode (AM). The AM RLC provides a retransmission function through an automatic repeat request (ARQ) for reliable data transmission. Meanwhile, a function of the RLC layer may be implemented with a functional block inside the MAC layer. In this case, the RLC layer may not exist.

A packet data convergence protocol (PDCP) layer belongs to the L2. The PDCP layer provides a function of header compression function that reduces unnecessary control information such that data being transmitted by employing IP packets, such as IPv4 or IPv6, can be efficiently transmitted over a radio interface that has a relatively small bandwidth. The header compression increases transmission efficiency in the radio section by transmitting only necessary information in a header of the data. In addition, the PDCP layer provides a function of security. The function of security includes ciphering which prevents inspection of third parties, and integrity protection which prevents data manipulation of third parties.

A radio resource control (RRC) layer belongs to the L3. The RLC layer is located at the lowest portion of the L3, and is only defined in the control plane. The RRC layer takes a role of controlling a radio resource between the UE and the network. For this, the UE and the network exchange an RRC message through the RRC layer. The RRC layer controls logical channels, transport channels, and physical channels in relation to the configuration, reconfiguration, and release of RBs. An RB is a logical path provided by the L1 and L2 for data delivery between the UE and the network. That is, the RB signifies a service provided the L2 for data transmission between the UE and E-UTRAN. The configuration of the RB implies a process for specifying a radio protocol layer and channel properties to provide a particular service and for determining respective detailed parameters and operations. The RB is classified into two types, i.e., a signaling RB (SRB) and a data RB (DRB). The SRB is used as a path for transmitting an RRC message in the control plane. The DRB is used as a path for transmitting user data in the user plane.

A Non-Access Stratum (NAS) layer placed over the RRC layer performs functions, such as session management and mobility management.

Referring to FIG. 2, the RLC and MAC layers (terminated in the eNB on the network side) may perform functions such as scheduling, automatic repeat request (ARQ), and hybrid automatic repeat request (HARQ). The RRC layer (terminated in the eNB on the network side) may perform functions such as broadcasting, paging, RRC connection management, RB control, mobility functions, and UE measurement reporting and controlling. The NAS control protocol (terminated in the MME of gateway on the network side) may perform functions such as a SAE bearer management, authentication, LTE IDLE mobility handling, paging origination in LTE IDLE, and security control for the signaling between the gateway and UE.

Referring to FIG. 3, the RLC and MAC layers (terminated in the eNB on the network side) may perform the same functions for the control plane. The PDCP layer (terminated in the eNB on the network side) may perform the user plane functions such as header compression, integrity protection, and ciphering.

Hereinafter, An RRC state of a UE and RRC connection procedure are described.

An RRC state indicates whether an RRC layer of the UE is logically connected to an RRC layer of the E-UTRAN. The RRC state may be divided into two different states such as an RRC connected state and an RRC idle state. When an RRC connection is established between the RRC layer of the UE and the RRC layer of the E-UTRAN, the UE is in RRC_CONNECTED, and otherwise the UE is in RRC_IDLE. Since the UE in RRC_CONNECTED has the RRC connection established with the E-UTRAN, the E-UTRAN may recognize the existence of the UE in RRC_CONNECTED and may effectively control the UE. Meanwhile, the UE in RRC_IDLE may not be recognized by the E-UTRAN, and a CN manages the UE in unit of a TA which is a larger area than a cell. That is, only the existence of the UE in RRC_IDLE is recognized in unit of a large area, and the UE must transition to RRC_CONNECTED to receive a typical mobile communication service such as voice or data communication.

In RRC_IDLE state, the UE may receive broadcasts of system information and paging information while the UE specifies a discontinuous reception (DRX) configured by NAS, and the UE has been allocated an identification (ID) which uniquely identifies the UE in a tracking area and may perform public land mobile network (PLMN) selection and cell reselection. Also, in RRC_IDLE state, no RRC context is stored in the eNB.

In RRC_CONNECTED state, the UE has an E-UTRAN RRC connection and a context in the E-UTRAN, such that transmitting and/or receiving data to/from the eNB becomes possible. Also, the UE can report channel quality information and feedback information to the eNB. In RRC_CONNECTED state, the E-UTRAN knows the cell to which the UE belongs. Therefore, the network can transmit and/or receive data to/from UE, the network can control mobility (handover and inter-radio access technologies (RAT) cell change order to GSM EDGE radio access network (GERAN) with network assisted cell change (NACC)) of the UE, and the network can perform cell measurements for a neighboring cell.

In RRC_IDLE state, the UE specifies the paging DRX cycle. Specifically, the UE monitors a paging signal at a specific paging occasion of every UE specific paging DRX cycle. The paging occasion is a time interval during which a paging signal is transmitted. The UE has its own paging occasion.

A paging message is transmitted over all cells belonging to the same tracking area. If the UE moves from one TA to another TA, the UE will send a tracking area update (TAU) message to the network to update its location.

When the user initially powers on the UE, the UE first searches for a proper cell and then remains in RRC_IDLE in the cell. When there is a need to establish an RRC connection, the UE which remains in RRC_IDLE establishes the RRC connection with the RRC of the E-UTRAN through an RRC connection procedure and then may transition to RRC_CONNECTED. The UE which remains in RRC_IDLE may need to establish the RRC connection with the E-UTRAN when uplink data transmission is necessary due to a user's call attempt or the like or when there is a need to transmit a response message upon receiving a paging message from the E-UTRAN.

To manage mobility of the UE in the NAS layer, two states are defined, i.e., an EPS mobility management-REGISTERED (EMM-REGISTERED) state and an EMM-DEREGISTERED state. These two states apply to the UE and the MME. Initially, the UE is in the EMM-DEREGISTERED state. To access a network, the UE performs a process of registering to the network through an initial attach procedure. If the attach procedure is successfully performed, the UE and the MME enter the EMM-REGISTERED state.

To manage a signaling connection between the UE and the EPC, two states are defined, i.e., an EPS connection management (ECM)-IDLE state and an ECM-CONNECTED state. These two states apply to the UE and the MME. When the UE in the ECM-IDLE state establishes an RRC connection with the E-UTRAN, the UE enters the ECM-CONNECTED state. When the MME in the ECM-IDLE state establishes an S1 connection with the E-UTRAN, the MME enters the ECM-CONNECTED state. When the UE is in the ECM-IDLE state, the E-UTRAN does not have context information of the UE. Therefore, the UE in the ECM-IDLE state performs a UE-based mobility related procedure such as cell selection or reselection without having to receive a command of the network. On the other hand, when the UE is in the ECM-CONNECTED state, mobility of the UE is managed by the command of the network. If a location of the UE in the ECM-IDLE state becomes different from a location known to the network, the UE reports the location of the UE to the network through a tracking area update procedure.

FIG. 4 shows a procedure in which UE that is initially powered on experiences a cell selection process, registers it with a network, and then performs cell reselection if necessary.

Referring to FIG. 4, the UE selects Radio Access Technology (RAT) in which the UE communicates with a Public Land Mobile Network (PLMN), that is, a network from which the UE is provided with service (S410). Information about the PLMN and the RAT may be selected by the user of the UE, and the information stored in a Universal Subscriber Identity Module (USIM) may be used.

The UE selects a cell that has the greatest value and that belongs to cells having measured BS and signal intensity or quality greater than a specific value (cell selection) (S420). In this case, the UE that is powered off performs cell selection, which may be called initial cell selection. A cell selection procedure is described later in detail. After the cell selection, the UE receives system information periodically by the BS. The specific value refers to a value that is defined in a system in order for the quality of a physical signal in data transmission/reception to be guaranteed. Accordingly, the specific value may differ depending on applied RAT.

If network registration is necessary, the UE performs a network registration procedure (S430). The UE registers its information (e.g., an IMSI) with the network in order to receive service (e.g., paging) from the network. The UE does not register it with a network whenever it selects a cell, but registers it with a network when information about the network (e.g., a Tracking Area Identity (TAI)) included in system information is different from information about the network that is known to the UE.

The UE performs cell reselection based on a service environment provided by the cell or the environment of the UE (S440). If the value of the intensity or quality of a signal measured based on a BS from which the UE is provided with service is lower than that measured based on a BS of a neighboring cell, the UE selects a cell that belongs to other cells and that provides better signal characteristics than the cell of the BS that is accessed by the UE. This process is called cell reselection differently from the initial cell selection of the No. 2 process. In this case, temporal restriction conditions are placed in order for a cell to be frequently reselected in response to a change of signal characteristic. A cell reselection procedure is described later in detail.

FIG. 5 shows an RRC connection establishment procedure.

The UE sends an RRC connection request message that requests RRC connection to a network (S510). The network sends an RRC connection establishment message as a response to the RRC connection request (S520). After receiving the RRC connection establishment message, the UE enters RRC connected mode.

The UE sends an RRC connection establishment complete message used to check the successful completion of the RRC connection to the network (S530).

FIG. 6 shows an RRC connection reconfiguration procedure.

An RRC connection reconfiguration is used to modify RRC connection. This is used to establish/modify/release RBs, perform handover, and set up/modify/release measurements.

A network sends an RRC connection reconfiguration message for modifying RRC connection to UE (S610). As a response to the RRC connection reconfiguration message, the UE sends an RRC connection reconfiguration complete message used to check the successful completion of the RRC connection reconfiguration to the network (S620).

The following is a detailed description of a procedure of selecting a cell by a terminal.

When power is turned-on or the terminal is located in a cell, the terminal performs procedures for receiving a service by selecting/reselecting a suitable quality cell.

A terminal in an RRC idle state should prepare to receive a service through the cell by always selecting a suitable quality cell. For example, a terminal where power is turned-on just before should select the suitable quality cell to be registered in a network. If the terminal in an RRC connection state enters in an RRC idle state, the terminal should selects a cell for stay in the RRC idle state. In this way, a procedure of selecting a cell satisfying a certain condition by the terminal in order to be in a service idle state such as the RRC idle state refers to cell selection. Since the cell selection is performed in a state that a cell in the RRC idle state is not currently determined, it is important to select the cell as rapid as possible. Accordingly, if the cell provides a wireless signal quality of a predetermined level or greater, although the cell does not provide the best wireless signal quality, the cell may be selected during a cell selection procedure of the terminal.

Hereinafter, a method and a procedure of selecting a cell by a terminal in a 3GPP LTE is described.

A cell selection process is basically divided into two types.

The first is an initial cell selection process. In this process, UE does not have preliminary information about a wireless channel. Accordingly, the UE searches for all wireless channels in order to find out a proper cell. The UE searches for the strongest cell in each channel. Thereafter, if the UE has only to search for a suitable cell that satisfies a cell selection criterion, the UE selects the corresponding cell.

Next, the UE may select the cell using stored information or using information broadcasted by the cell. Accordingly, cell selection may be fast compared to an initial cell selection process. If the UE has only to search for a cell that satisfies the cell selection criterion, the UE selects the corresponding cell. If a suitable cell that satisfies the cell selection criterion is not retrieved though such a process, the UE performs an initial cell selection process.

After the UE selects a specific cell through the cell selection process, the intensity or quality of a signal between the UE and a BS may be changed due to a change in the mobility or wireless environment of the UE. Accordingly, if the quality of the selected cell is deteriorated, the UE may select another cell that provides better quality. If a cell is reselected as described above, the UE selects a cell that provides better signal quality than the currently selected cell. Such a process is called cell reselection. In general, a basic object of the cell reselection process is to select a cell that provides UE with the best quality from a viewpoint of the quality of a radio signal.

In addition to the viewpoint of the quality of a radio signal, a network may determine priority corresponding to each frequency, and may inform the UE of the determined priorities. The UE that has received the priorities preferentially takes into consideration the priorities in a cell reselection process compared to a radio signal quality criterion.

As described above, there is a method of selecting or reselecting a cell according to the signal characteristics of a wireless environment. In selecting a cell for reselection when a cell is reselected, the following cell reselection methods may be present according to the RAT and frequency characteristics of the cell.

-   -   Intra-frequency cell reselection: UE reselects a cell having the         same center frequency as that of RAT, such as a cell on which         the UE camps on.     -   Inter-frequency cell reselection: UE reselects a cell having a         different center frequency from that of RAT, such as a cell on         which the UE camps on     -   Inter-RAT cell reselection: UE reselects a cell that uses RAT         different from RAT on which the UE camps

The principle of a cell reselection process is as follows.

First, UE measures the quality of a serving cell and neighbor cells for cell reselection.

Second, cell reselection is performed based on a cell reselection criterion. The cell reselection criterion has the following characteristics in relation to the measurements of a serving cell and neighbor cells.

Intra-frequency cell reselection is basically based on ranking. Ranking is a task for defining a criterion value for evaluating cell reselection and numbering cells using criterion values according to the size of the criterion values. A cell having the best criterion is commonly called the best-ranked cell. The cell criterion value is based on the value of a corresponding cell measured by UE, and may be a value to which a frequency offset or cell offset has been applied, if necessary.

Inter-frequency cell reselection is based on frequency priority provided by a network. UE attempts to camp on a frequency having the highest frequency priority. A network may provide frequency priority that will be applied by UEs within a cell in common through broadcasting signaling, or may provide frequency-specific priority to each UE through UE-dedicated signaling. A cell reselection priority provided through broadcast signaling may refer to a common priority. A cell reselection priority for each terminal set by a network may refer to a dedicated priority. If receiving the dedicated priority, the terminal may receive a valid time associated with the dedicated priority together. If receiving the dedicated priority, the terminal starts a validity timer set as the received valid time together therewith. While the valid timer is operated, the terminal applies the dedicated priority in the RRC idle mode. If the valid timer is expired, the terminal discards the dedicated priority and again applies the common priority.

For the inter-frequency cell reselection, a network may provide UE with a parameter (e.g., a frequency-specific offset) used in cell reselection for each frequency.

For the intra-frequency cell reselection or the inter-frequency cell reselection, a network may provide UE with a Neighboring Cell List (NCL) used in cell reselection. The NCL includes a cell-specific parameter (e.g., a cell-specific offset) used in cell reselection.

For the intra-frequency or inter-frequency cell reselection, a network may provide UE with a cell reselection black list used in cell reselection. The UE does not perform cell reselection on a cell included in the black list.

Ranking performed in a cell reselection evaluation process is described below.

A ranking criterion used to apply priority to a cell is defined as in Equation 1. R _(S) =Q _(meas,s) +Q _(hyst) ,R _(n) =Q _(meas,n) −Q _(offset)  [Equation 1]

In this case, Rs is the ranking criterion of a serving cell, Rn is the ranking criterion of a neighbor cell, Qmeas,s is the quality value of the serving cell measured by UE, Qmeas,n is the quality value of the neighbor cell measured by UE, Qhyst is the hysteresis value for ranking, and Qoffset is an offset between the two cells.

In Intra-frequency, if UE receives an offset “Qoffsets,n” between a serving cell and a neighbor cell, Qoffset=Qoffsets,n. If UE does not Qoffsets,n, Qoffset=0.

In Inter-frequency, if UE receives an offset “Qoffsets,n” for a corresponding cell, Qoffset=Qoffsets,n+Qfrequency. If UE does not receive “Qoffsets,n”, Qoffset=Qfrequency.

If the ranking criterion Rs of a serving cell and the ranking criterion Rn of a neighbor cell are changed in a similar state, ranking priority is frequency changed as a result of the change, and UE may alternately reselect the twos. Qhyst is a parameter that gives hysteresis to cell reselection so that UE is prevented from to alternately reselecting two cells.

UE measures RS of a serving cell and Rn of a neighbor cell according to the above equation, considers a cell having the greatest ranking criterion value to be the best-ranked cell, and reselects the cell. If a reselected cell is not a suitable cell, UE excludes a corresponding frequency or a corresponding cell from the subject of cell reselection.

FIG. 7 shows an RRC connection re-establishment procedure.

Referring to FIG. 7, UE stops using all the radio bearers that have been configured other than a Signaling Radio Bearer (SRB) #0, and initializes a variety of kinds of sublayers of an Access Stratum (AS) (S710). Furthermore, the UE configures each sublayer and the PHY layer as a default configuration. In this procedure, the UE maintains the RRC connection state.

The UE performs a cell selection procedure for performing an RRC connection reconfiguration procedure (S720). The cell selection procedure of the RRC connection re-establishment procedure may be performed in the same manner as the cell selection procedure that is performed by the UE in the RRC idle state, although the UE maintains the RRC connection state.

After performing the cell selection procedure, the UE determines whether or not a corresponding cell is a suitable cell by checking the system information of the corresponding cell (S730). If the selected cell is determined to be a suitable E-UTRAN cell, the UE sends an RRC connection re-establishment request message to the corresponding cell (S740).

Meanwhile, if the selected cell is determined to be a cell that uses RAT different from that of the E-UTRAN through the cell selection procedure for performing the RRC connection re-establishment procedure, the UE stops the RRC connection re-establishment procedure and enters the RRC idle state (S750).

The UE may be implemented to finish checking whether the selected cell is a suitable cell through the cell selection procedure and the reception of the system information of the selected cell. To this end, the UE may drive a timer when the RRC connection re-establishment procedure is started. The timer may be stopped if it is determined that the UE has selected a suitable cell. If the timer expires, the UE may consider that the RRC connection re-establishment procedure has failed, and may enter the RRC idle state. Such a timer is hereinafter called an RLF timer. In LTE spec TS 36.331, a timer named “T311” may be used as an RLF timer. The UE may obtain the set value of the timer from the system information of the serving cell.

If an RRC connection re-establishment request message is received from the UE and the request is accepted, a cell sends an RRC connection re-establishment message to the UE.

The UE that has received the RRC connection re-establishment message from the cell reconfigures a PDCP sublayer and an RLC sublayer with an SRB1. Furthermore, the UE calculates various key values related to security setting, and reconfigures a PDCP sublayer responsible for security as the newly calculated security key values. Accordingly, the SRB1 between the UE and the cell is open, and the UE and the cell may exchange RRC control messages. The UE completes the restart of the SRB1, and sends an RRC connection re-establishment complete message indicative of that the RRC connection re-establishment procedure has been completed to the cell (S760).

In contrast, if the RRC connection re-establishment request message is received from the UE and the request is not accepted, the cell sends an RRC connection re-establishment reject message to the UE.

If the RRC connection re-establishment procedure is successfully performed, the cell and the UE perform an RRC connection reconfiguration procedure. Accordingly, the UE recovers the state prior to the execution of the RRC connection re-establishment procedure, and the continuity of service is guaranteed to the upmost.

Hereinafter, a D2D operation will be described. In the 3GPP LTE-A, a service related to the D2D operation refers to Proximity based Services (ProSe). Hereinafter, the ProSe is an equivalent concept with the D2D operation and the ProSe may be compatibly used with the D2D operation. The ProSe is now described. The ProSe includes ProSe direct communication and ProSe direct discovery.

The ProSe direct communication presents communication performed by two or more adjacent terminals. The terminals may perform communication using a protocol of a user plane. A ProSe-enabled UE means a UE for supporting a process related to requirements of the ProSe. Unless otherwise defined, the ProSe-enabled UE includes both of a public safety UE and a non-public safety UE. The public safety UE represents a UE for supporting both of a public safety specified function and the ProSe process. The non-public safety UE is a terminal which supports the ProSe process but does not support the public safety specified function.

The ProSe direct discovery is a process where the ProSe-enabled UE discovers another ProSe-enabled UE. In this case, only ability of the two ProSe-enabled UEs is used. An EPC-level ProSe discovery signifies a process where an EPC determines whether 2 ProSe enable terminals are closed to each other, and reports the close state thereof the two ProSe enabled terminals. Hereinafter, the ProSe direct communication may refer to D2D communication, and the ProSe direct discovery may refer to D2D discovery.

FIG. 8 shows a reference structure for a ProSe.

Referring to FIG. 8, the reference structure for a ProSe includes a plurality of terminals having E-UTRAN, EPC, and ProSe application program, a ProSe application (APP) server, and a ProSe function. An EPC is a representative example of the E-UTRAN. The EPC may include an MME, an S-GW, a P-GW, a policy and charging rules function (PCRF), and a home subscriber server (HSS). The ProSe application server is a user of ProSe in order to make an application function. The ProSe application server may communicate with an application program in the terminal. The application program in the terminal may use a ProSe ability to make an application function.

The ProSe function may include at least one of following functions but is not limited thereto.

-   -   Interworking via a reference point towards the 3rd party         applications     -   Authorization and configuration of the UE for discovery and         direct communication)     -   Enable the function of the EPC level ProSe discovery     -   ProSe related new subscriber data and handling of data storage,         and also handling of ProSe identities     -   Security related function     -   Provide control towards the EPC for policy related function     -   Provide function for charging (via or outside of EPC, e.g.,         offline charging))

Hereinafter, a reference point and a reference interface will be described in a reference structure for the ProSe.

-   -   PC1: a reference point between a ProSe application program in         the terminal and a ProSe application program in a ProSe         application server. The PC1 is used to define signaling         requirements in an application level.     -   PC2: is a reference point between the ProSe application server         and a ProSe function. The PC2 is used to define an interaction         between the ProSe application server and a ProSe function. An         application data update of a ProSe database of the ProSe         function may be an example of the interaction.     -   PC3: is a reference point between the terminal and the ProSe         function. The PC3 is used to define an interaction between the         terminal and the ProSe function. Configuration for ProSe         discovery and communication may be an example of the         interaction.     -   PC4: is a reference point between an EPC and the ProSe function.         The PC4 is used to define an interaction between the EPC and the         ProSe function. The interaction lay illustrate when a path for         1:1 communication or a ProSe service for real time session         management or mobility management are authorized.     -   PC5: is a reference point to use control/user plane for         discovery, communication, and relay between terminals, and 1:1         communication.     -   PC6: is a reference point to use a function such as ProSe         discovery between users included in different PLMNs.     -   SGi: may be used for application data and application level         control information exchange.

Hereinafter, ProSe Direct Communication (D2D Communication) is described.

The ProSe direct communication is a communication mode where two public safety terminals may perform direct communication through a PC 5 interface. The communication mode may be supported in both of a case of receiving a service in coverage of E-UTRAN or a case of separating the coverage of E-UTRAN.

FIG. 9 shows arrangement examples of terminals performing ProSe direct communication and cell coverage.

Referring to FIG. 9(a), UEs A and B may be located outside of the cell coverage. Referring to FIG. 9(b), the UE A may be located in the cell coverage and the UE B may be located outside of the cell coverage. Referring to FIG. 9(c), both of UEs A and B may be located in the cell coverage. Referring to FIG. 9(d), the UE A may be located in coverage of a first cell and the UE B may be in coverage of a second cell. As described above, the ProSe direct communication may be performed between terminals which are provided at various positions.

Meanwhile, following IDs may be used in the ProSe direct communication.

-   -   Source layer-2 ID: The source layer-2 ID identifies a sender of         a packet in a PC 5 interface.     -   Purpose layer-2 ID: The purpose layer-2 ID identifies a target         of a packet in a PC 5 interface.     -   SA L1 ID: The SA L1 ID represents an in an ID in a scheduling         assignment (SA) in the PC 5 interface.

FIG. 10 shows a user plane protocol stack for the ProSe direct communication.

Referring to FIG. 10, the PC 5 interface includes a PDCH layer, a RLC layer, a MAC layer, and a PHY layer. There may not be HARQ feedback in the ProSe direct communication. An MAC header may include the source layer-2 ID and the purpose layer-2 ID.

Hereinafter, Radio Resource Assignment for ProSe Direct Communication is described. A ProSe enable terminal may use following two modes with respect to resource assignments for the ProSe direct communication.

1) Mode 1: The mode 1 is a mode for receiving scheduling a resource for the ProSe direct communication from a base station. The terminal should be in a RRC_CONNECTED state according to the mode 1 in order to transmit data. The terminal requests a transmission resource to the base station, and the base station schedules a resource for scheduling assignment and data transmission. The terminal may transmit a scheduling request to the base station and may transmit a Buffer Status Report (ProSe BSR). The base station has data which the terminal will perform the ProSe direct communication and determines whether a resource for transmitting the data is required.

2) Mode 2: The mode 2 is a mode for selecting a direct resource. The terminal directly selects a resource for the ProSe direct communication from a resource pool. The resource pool may be configured by a network or may be previously determined.

Meanwhile, when the terminal includes a serving cell, that is, when the terminal is in an RRC_CONNECTED state with the base station or is located in a specific cell in an RRC_IDLE state, the terminal is regarded to be in coverage of the base station. If the terminal is located outside of the coverage, only the mode 2 is applicable. If the terminal is located in the coverage, the mode 1 or the mode 2 may be used according to setting of the base station. If there are no exceptional conditions, only when the base station is configured, the terminal may change a mode from the mode 1 to the mode 2 or from the mode 2 to the mode 1.

Hereinafter, ProSe Direct Discovery (D2D Discovery) is described.

The ProSe direct discovery represents a process used to discover when the ProSe enabled terminal discovers other neighboring ProSe enabled terminal and refers to D2D direction discovery or D2D discovery. In this case, an E-UTRA wireless signal through the PC 4 interface may be used. Hereinafter, information used for the ProSe direct discovery refers to discovery information.

FIG. 11 shows a PC 5 interface for D2D discovery.

Referring to FIG. 11, the PC 5 interface includes an MAC layer, a PHY layer, and a ProSe Protocol layer being an upper layer. Permission for announcement and monitoring of discovery information is handled in the upper layer ProSe Protocol. Contents of discovery information are transparent to an access stratum (AS). The ProSe Protocol allows only valid discovery information to be transferred to the AS for announcement.

An MAC layer receives discovery information from the upper layer ProSe Protocol. An IP layer is not used for transmitting the discovery information. The MAC layer determines a resource used in order to announce the discovery information received from the upper layer. The MAC layer makes and sends a protocol data unit (MAC PDU) to a physical layer. An MAC header is not added.

There are two types of resource assignments for announcing the discovery information.

1) Type 1: The type 1 is a method assigned so that resources for announcing the discovery information are not terminal-specific and the base station provides resource pool configuration for announcing the discovery information to the terminals. The configuration may be included in a system information block (SIB) to be signaled in a broadcast scheme. Alternatively, the configuration may be included in a terminal specific RRC message to be provided. Alternatively, the configuration may be broadcast-signaled or terminal-specific signaled of a different layer from the RRC message. The terminal selects a resource from an indicated resource pool to announce discovery information using the selected resource. The terminal may announce discovery information through a resource optionally selected during each discovery period.

2) Type 2: The type 2 is a method where resources for announcing the discovery information are terminal-specifically assigned. A terminal in a RRC_CONNECTED state may request a resource for announcing a discovery signal to the base station through a RRC signal. The base station may assign a resource for announcing a discovery signal as an RRC signal. A resource for monitoring the discovery signal in a configured resource pool may be assigned in terminals.

With respect to a terminal in an RRC_IDLE state, a base station may report a type 1 resource pool for announcing the discovery signal as an SIB. Terminals where ProSe direct discovery is allowed use a type 1 resource pool for announcing the discovery information in the RRC_IDLE state. Alternatively, the base station 2) reports that the base station supports the ProSe direct discovery through the SIB but may not provide the resource for announcing the discovery information. In this case, the terminal should enter the RRC_CONNECTED state for announcing the discovery information.

With respect to a terminal in an RRC_CONNECTED state, the base station may configure whether to use a type 1 resource pool or a type 2 resource pool for announcing the discovery information through a RRC signal.

FIG. 12 shows an embodiment of a ProSe direct discovery procedure.

Referring to FIG. 12, it is assumed in a terminal A and a terminal B that a ProSe-enabled application program is operated, and the terminal A and the terminal B are configured in a friend relationship to each other, that is, a relationship capable of allowing D2D communication with each other in the application program. Hereinafter, the terminal B may be expressed as a friend of the terminal A. For example, the application program may be a social networking program. 3GPP Layers correspond to functions of an application program for using a ProSe discovery service regulated according to 3GPP.

A ProSe direct discovery between the terminal A and the terminal B may perform a following procedure.

1) First, the terminal A performs regular application-Layer communication with an application server. The above communication is performed based on Application programming interface (API).

2) A ProSe enabled application program of the terminal A receives a list of application layer IDs having a friend relationship. The application layer ID may generally be in the form of a network access ID. For example, an application layer ID of the terminal A may have a form such as adam@example.com.

3) A terminal A requests private expression codes for a user and private expression codes for a friend of the user.

4) 3GPP layers transmit an expression code request to a ProSe server.

5) The ProSe server map application layer IDs provided from an operator or a third application server to private expression codes. For example, an application layer ID such as adam@example.com. The mapping may be performed based on parameters (e.g., mapping algorithms, key values, and the like) received from an application service of the network.

6) The ProSe server responds the obtained expression codes to the 3GPP layers. The 3GPP layers report that expression codes with respect to the requested application layer are successively received to the ProSe enabled application program. Further, a mapping table between the application layer IDs and the expression codes are generated.

7) The ProSe enabled application program requests the 3GPP layers to start the discovery procedure. That is, when one of friends is located close to the terminal A and direct communication may be performed, the ProSe enabled application program attempts the discovery. 3GPP layers announce a private expression code of the terminal A (that is, “GTER543$#2FSJ67DFSF” which is a private expression code of adam@example.com in the above example). In mapping of an application layer ID of a corresponding application program and the private expression code, the mapping relationship may be known by the previously received friends, and the mapping may be performed.

8) It is assumed that the terminal B is operating the same ProSe enabled application program as that of the terminal A, and the above steps 3 to 6 may be executed. 3GPP layers included in the terminal B may perform ProSe discovery.

9) When the terminal B receives the above announce from the terminal A, the terminal B determines whether the private expression code included in the announce is known by the terminal B or is mapped to an application layer ID. As illustrated in step 8, since the terminal B performs steps 3 to 6, the terminal B knows a private expression code with respect to the terminal A, mapping of the private expression code to the application layer ID, and which is a corresponding application program. Accordingly, the terminal B may discover the terminal B from the announce of the terminal A. The 3GPP layers in the terminal B announces that adam@example.com is discovered to the ProSe enable application program.

FIG. 12 shows a discovery procedure by taking into consideration the terminals A and B, the ProSe server, and the application server. Only an operation side between the terminals A and B is described. The terminal A transmits a signal called the announce (the procedure may refer to announcement), and the terminal B receives the announce to discover the terminal A. That is, a discovery procedure of FIG. 12 in an operation directly related to another terminal among operations performed by each terminal may refer to a single step discovery procedure may refer to a single step discovery procedure in a side of one step.

FIG. 13 shows another embodiment of a ProSe direct discovery procedure.

In FIG. 13, it is assumed that the terminal 1 to the terminal 4 may be included in a specific group communication system enablers (GCSE) group. It is assumed that the terminal 1 is a discoverer and terminals 2, 3, and 4 are a discoveree. A terminal 5 is a terminal regardless of a discovery procedure.

The terminal 1 and the terminals 2 to 4 may perform a following operation in a discovery procedure. First, the terminal 1 broadcasts a targeted discovery request message (hereinafter referred to ‘discovery request message’ or ‘M1’) in order to discover whether an optional terminal included in the GCSE group is located around the terminal 1. The targeted discovery request message may include a unique application program group ID or a layer-2 group ID of the specific GCSE group. Further, the targeted discovery request message may include a unique ID of the terminal 1, that is, an application program private ID. The targeted discovery request message may be received by the terminals.

The terminal 5 transmits no response messages. The terminals 2, 3, and 4 included in the GCSE group transmit a targeted discovery response message (hereinafter referred to as a discovery response message or M2) as a response to the targeted discovery request message. The targeted discovery response message may include a unique application program private ID of a terminal transmitting the message.

An operation of terminals in a ProSe discovery procedure illustrated in FIG. 13 will be described. A discoverer (UE 1) transmits the targeted discovery request message, and receives a targeted discovery response message being a response thereto. In addition, if a discoveree (e.g., UE 2) receives the targeted discovery request message, the discoveree transmits a targeted discovery response message as a response thereto. Accordingly, each terminal performs an operation a second step. In the above side, a ProSe discovery procedure of FIG. 13 may refer to a discovery procedure.

In addition to the discovery procedure illustrated in FIG. 13, if the terminal 1 (discoverer) transmits a discovery confirm message (hereinafter may refer to M3) as a response to the targeted discovery response message, this may refer to a third step discovery procedure.

FIG. 14 shows a problem which may occur in the conventional V2X communication.

When an event such as a vehicle collision occurs, this may be transmitted between a base station and a road side unit (RSU) so that the event is indicated rapidly to an adjacent region. For this, the base station or the RSU may periodically broadcast event-related information to a terminal in coverage. However, since the base station or the RSU cannot know an event termination time if the event is terminated, it may be problematic for the base station or the RSU to continuously broadcast the event-related information after the event is terminated. Further, the base station or the RSU may need to propagate an event occurring according to a range of the event-related information to a wide region.

More specifically, referring to FIG. 14, it is assumed that a vehicle collision has occurred in a region of a second base station. Accordingly, the vehicle in which the collision occurs may transmit event occurrence information to the second base station. Upon receiving the event occurrence information, the second base station may transmit the event occurrence information to a third base station which is a neighboring base station, and a vehicle A which has received the event occurrence information from the third base station may know that the vehicle has collided in a specific duration.

However, it may be problematic if the second base station which does not know that the event is terminated periodically transmits the event occurrence information to the third base station even if the event is terminated due to completion of accident handling or the like.

In addition, in case of a vehicle B located in a region of a fourth base station, since the event occurrence information cannot be received, it may be necessary to propagate the event occurrence information to the vehicle B located in a wider region (i.e., a region of the fourth base station).

Since there is no procedure for solving such a problem in the conventional V2X, the present invention proposes a method for solving the aforementioned problem.

FIG. 15 shows a method by which a base station or an RSU indicates an event termination according to an embodiment of the present invention.

Referring to FIG. 15, the base station or the RSU may indicate that an event is terminated to a neighboring base station or a neighboring RSU having an X2 connectivity.

An event such as a vehicle collision accident may occur in a first terminal (S1500). The first terminal may be a terminal equipped in a vehicle for V2X.

In order to rapidly propagate the event to an adjacent region, the first terminal may transmit event occurrence information to a first base station or a first RSU (S1510). The event occurrence information may be transmitted periodically.

The first base station or the first RSU may provide a second base station or a second RSU with information regarding an event which has occurred in the first terminal by using a new IE included in an event occurrence indication message, an existing message, a new IE included in a new message, or a new IE included in the existing message (S1520).

When the second base station or the second RSU receives a message from the first base station or the first RSU, the second base station or the second RSU may broadcast the event occurrence information to a terminal in coverage including a second terminal (S1530). For example, the second terminal and the terminal in the coverage of the second terminal may know that a collision event has occurred in a vehicle equipped in the first terminal.

Thereafter, event processing may be complete in the first terminal (S1540).

Therefore, the first terminal may transmit event termination information to the first base station or the first RSU (S1550). The event termination information may be information indicating that collision accident handling or the like is complete and thus the event is terminated. If the first base station or the first RSU has event occurrence information transmitted periodically, transmission of the event occurrence information may stop. That is, upon receiving the event termination information, the first base station or the first RSU may not transmit the event occurrence information any more to the second base station or the second RSU.

Upon receiving information regarding an event termination, the first base station or the first RSU may provide the second base station or the second RSU with the event termination information by using a new IE included in an event termination indication message, an existing message, a new IE included in a new message, or a new IE included in the existing message (S1560).

If the event occurrence information is no longer received in the first base station or the first RSU during a specific time, the first base station or the first RSU may provide the second base station or the second RSU with the event termination information by using a new IE included in an event termination indication message, an existing message, a new IE included in a new message, or a new IE included in the existing message.

According to an embodiment of the present invention, it is possible to solve a problem in that the first base station or first RSU which does not know that the event is terminated transmits event occurrence information periodically to the second base station or the second RSU even if the event is terminated due to completion of accident handling or the like.

FIG. 16 shows a method by which a base station or an RSU indicates an event type and a hop level according to an embodiment of the present invention.

Referring to FIG. 16, the base station or the RSU may indicate event occurrence type information and a hop level to a neighboring base station or a neighboring RSU having an X2 connectivity. The event occurrence type information is information regarding a range in which the event occurrence information is necessarily propagated. The event occurrence type information is information regarding a range in which the event termination information is necessarily propagated. The hop level may be the maximum number of base stations or RSUs to which the event occurrence type information is necessarily propagated. For example, it may be the maximum number of base stations or RSUs via which the event occurrence information necessarily passes if a collision accident occurs in a vehicle having a V2X terminal installed therein. Alternatively, it may be the maximum number of base stations or RSUs via which the event termination information necessarily pass if handling of the collision accident occurring in the vehicle having the V2X terminal installed therein is complete.

An event such as a vehicle collision accident, completion of vehicle collision accident handling, or the like may occur in the first terminal (S1600). The first terminal may be a terminal equipped in a vehicle for V2X.

According to a range of accidents, the first terminal may transmit event occurrence/termination information including event occurrence type information to the first base station or the first RSU (S1610).

On the basis of the event occurrence type information received from the first terminal, the first base station or the first RSU may generate a hop level (S1620). In addition, the first base station or the first RSU may store the generated hop level.

The first base station or the first RSU may transmit an event indication message including the event occurrence type information and the hop level, an existing message, a new IE included in a new message, or a new IE included in the existing message to a second base station or a second RSU (S1630).

If the first base station or the first RSU receives the event indication message, the second base station or the second RSU may decrease the received hop level by 1, and may check whether the modified hop level is equal to a predefined value (S1640). The predefined value may be 1. Alternatively, the predefined value may be 0. If the modified hop level is equal to the predefined value, the second base station or the second RSU may not transmit a message to the neighboring base station or the neighboring RSU but broadcast event occurrence information or event termination information including the event occurrence type information to a terminal in coverage.

If the modified hop level is not equal to the predefined value, the second base station or the second RSU may transmit an event indication message including the event occurrence type information or the modified hop level, an existing message, a new IE included in a new message, or a new IE included in the existing message to a third base station or a third RSU (S1650).

If the second base station or the second RSU receives the event indication message, the third base station or the third RSU may decrease the modified hop level by 1, and may check whether the modified hop level is equal to a predefined value (S1660). That is, the third base station or the third RSU may perform the same step as S1640.

If the modified hop level is equal to the predefined value, the third base station or the third RSU may broadcast the event occurrence/termination information including the event occurrence type information to the terminal in coverage (S1670). That is, the event occurrence/termination information may be broadcast to the second terminal in coverage.

In the method of FIG. 16, if the event termination indication message proposed in the method of FIG. 15 is used to indicate the event termination, the hop level stored in the first base station or the first RSU may be transmitted together with the event termination indication message.

FIG. 17 shows a path of transmitting a message between a base station or an RSU and a neighboring base station or a neighboring RSU according to an embodiment of the present invention.

Referring to FIG. 17, a first/second base station or a first/second RSU may include a V2X server, an S/P-GW connected to the V2X server, a BM-SC connected to the V2X server, and an MBMS-GW connected to the BM-SC. The event occurrence indication or event termination indication described in FIG. 15 and the event indication including event occurrence type information or the hop level described in FIG. 16 may be transmitted from the base station or the RSU to the neighboring base station or the neighboring RSU by using the following method. For convenience of explanation, the base station or the RSU is called the first base station or the first RSU, and the neighboring base station or the neighboring RSU is called the second base station or the second RSU.

Referring to first signaling of FIG. 17, in case of signaling between the V2X server of the first base station or the first RSU and the V2X server of the second base station or the second RSU, the event occurrence indication, the event termination indication, or the event indication may be transmitted through a new message.

Referring to second signaling of FIG. 17, in case of signaling between the V2X server of the first base station or the first RSU and the BM-SC of the second base station or the second RSU, the event occurrence indication, the event termination indication, or the event indication may be transmitted through at least any one of a deallocate TMGI request message, a modify MBMS bearer request message, a deactivate MBMS bearer request message, and a new message.

Referring to third signaling of FIG. 17, in case of signaling between the BM-SC of the first base station or the first RSU and the MBMS-GW of the second base station or the second RSU, the event occurrence indication, the event termination indication, or the event indication may be transmitted through at least any one of an MBMS session update request message, an MBMS session stop request message, and a new message.

FIG. 18 is a block diagram of a method by which a device performs V2X communication according to an embodiment of the present invention.

Referring to FIG. 18, the device may receive event termination information from a terminal (S1810). The device may be a base station. The device may be an RSU. The terminal may be a terminal installed in a vehicle for V2X communication. The event termination information may be information indicating that an event occurring in the terminal has been terminated.

The device may transmit the event termination information to a neighboring device (S1820). The device and the neighboring device may be connected through X2. The event termination information may be transmitted by being included in at least any one of an event termination indication message, an existing message, a new IE included in a new message, or a new IE included in the existing message. The event termination information may be transmitted by being included in at least any one of a deallocate TMGI request message, a modify MBMS bearer request message, a deactivate MBMS bearer request message, an MBMS session update request message, an MBMS session stop request message, and a new message.

The device may receive the event occurrence information from the terminal, and may transmit the event occurrence information to the neighboring device. The event occurrence information may be information indicating that an event has occurred in the terminal. If the device which has received the event termination information has the event occurrence information, transmission of the event occurrence information to the neighboring device may stop.

The device may generate a hop level, and may transmit the hop level to the neighboring device. The device may store the hop level. The hop level may indicate the number of devices via which the event occurring in the terminal passes.

FIG. 19 is a block diagram of a method by which a device performs V2X communication according to an embodiment of the present invention.

Referring to FIG. 19, a first device may receive a hop level from a second device (S1910). The hop level may indicate the number of devices via which the event occurrence type information passes. The terminal may be a terminal installed in a vehicle for V2X communication. The event occurrence type information is information regarding a range in which the event occurrence information is propagated. The event occurrence type information is information regarding a range in which the event termination information is propagated.

The first device may modify the received hop level (S1920). The modifying of the hop level may be decreasing of the hop level by 1.

The first device may compare the modified hope level with a predefined value (S1930). The predefined value may be 0. Alternatively, the predefined value may be 1.

The first device may broadcast the event occurrence type information to a terminal in coverage of the first device if the modified hop level is equal to the predefined value, and may transmit the event occurrence type information and the modified hop level to a third device if the modified hop level is different from the predefined value (S1940). The second device and the third device may be connected with the first device through X2. The first device, the second device, and the third device may be any one of a base station and an RSU.

FIG. 20 is a block diagram illustrating a wireless communication system according to the embodiment of the present invention.

A BS 2000 includes a processor 2001, a memory 2002 and a transceiver 2003. The memory 2002 is connected to the processor 2001, and stores various information for driving the processor 2001. The transceiver 2003 is connected to the processor 2001, and transmits and/or receives radio signals. The processor 2001 implements proposed functions, processes and/or methods. In the above embodiment, an operation of the base station may be implemented by the processor 2001.

A UE 2010 includes a processor 2011, a memory 2012 and a transceiver 2013. The memory 2012 is connected to the processor 2011, and stores various information for driving the processor 2011. The transceiver 2013 is connected to the processor 2011, and transmits and/or receives radio signals. The processor 2011 implements proposed functions, processes and/or methods. In the above embodiment, an operation of the UE may be implemented by the processor 2011.

The processor may include an application-specific integrated circuit (ASIC), a separate chipset, a logic circuit, and/or a data processing unit. The memory may include a read-only memory (ROM), a random access memory (RAM), a flash memory, a memory card, a storage medium, and/or other equivalent storage devices. The transceiver may include a base-band circuit for processing a wireless signal. When the embodiment is implemented in software, the aforementioned methods can be implemented with a module (i.e., process, function, etc.) for performing the aforementioned functions. The module may be stored in the memory and may be performed by the processor. The memory may be located inside or outside the processor, and may be coupled to the processor by using various well-known means.

Various methods based on the present specification have been described by referring to drawings and reference numerals given in the drawings on the basis of the aforementioned examples. Although each method describes multiple steps or blocks in a specific order for convenience of explanation, the invention disclosed in the claims is not limited to the order of the steps or blocks, and each step or block can be implemented in a different order, or can be performed simultaneously with other steps or blocks. In addition, those ordinarily skilled in the art can know that the invention is not limited to each of the steps or blocks, and at least one different step can be added or deleted without departing from the scope and spirit of the invention.

The aforementioned embodiment includes various examples. It should be noted that those ordinarily skilled in the art know that all possible combinations of examples cannot be explained, and also know that various combinations can be derived from the technique of the present specification. Therefore, the protection scope of the invention should be determined by combining various examples described in the detailed explanation, without departing from the scope of the following claims. 

What is claimed is:
 1. A method for performing, by a first road side unit (RSU), V2X communication in a wireless communication system, the method comprising: receiving event occurrence information and a hop level, from a second RSU, wherein the hop level is generated by the second RSU based on a type of the event occurrence information received from a first user equipment (UE); decreasing of the received hop level by one; when the decreased hop level is zero: broadcasting the event occurrence information to a second UE in a coverage of the first RSU, and wherein the event occurrence information and the decreased hop level are not transmitted to a third RSU located in a neighbor of the first RSU; and when the decreased hop level is larger than zero: broadcasting the event occurrence information to the second UE in the coverage of the first RSU, and transmitting the event occurrence information and the decreased hop level to the third RSU, wherein the first UE and the second UE are included in vehicles, and wherein the second RSU and the third RSU are connected with the first RSU.
 2. The method of claim 1, wherein the type of the event occurrence information includes a range in which the event occurrence information is propagated.
 3. The method of claim 1, further comprising: receiving event termination information and the hop level, from the second RSU.
 4. The method of claim 1, wherein the event occurrence information and the hop level are transmitted by being included in at least one of an event indication message, a deallocate temporary mobile group identify (TMGI) request message, a modify multimedia broadcast multicast service (MBMS) bearer request message, a deactivate MBMS bearer request message, an MBMS session update request message, an MBMS session stop request message, or a new message.
 5. A first road side unit (RSU) performing V2X communication in a wireless communication system, the first RSU comprising: a memory; a transceiver; and a processor operatively coupled to the memory and the transceiver, wherein the processor is configured to: control the transceiver to receive event occurrence information and a hop level, from a second RSU, wherein the hop level is generated by the second RSU based on a type of the event occurrence information received from a first user equipment (UE); decrease of the received hop level by one; when the decreased hop level is zero: control the transceiver to broadcast the event occurrence information to a second UE in a coverage of the first RSU, and wherein the event occurrence information and the decreased hop level are not transmitted to a third RSU located in a neighbor of the first RSU; and when the decreased hop level is larger than zero: control the transceiver to broadcast the event occurrence information to a second UE in a coverage of the first RSU, and control the transceiver to transmit the event occurrence information and the decreased hop level to the third RSU, wherein the first UE and the second UE are included in vehicles, and wherein the second RSU and the third RSU are connected with the first RSU.
 6. The first RSU of claim 5, wherein the type of the event occurrence information includes a range in which the event occurrence information is propagated. 